1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method, and more particularly to a substrate processing apparatus suitable for use in etching or cleaning a peripheral portion or an opposite surface of a semiconductor substrate at a high level of cleanliness.
2. Description of the Related Art
In recent years, attention has been drawn to technologies for embedding an interconnection material in trenches on semiconductor substrates to form damascene interconnections of copper, for example. It has also been attempted in the art to form capacitor electrodes having a high dielectric constant in semiconductor substrates. In either case, a desired metal or metal compound is deposited as a thin film on a surface of a semiconductor substrate by sputtering or the like. At this time, the thin film is deposited not only on the surface of the semiconductor substrate, but also on a bevel portion of a peripheral portion and an opposite surface of the semiconductor substrate. Contamination of the bevel portion and the opposite surface with metal or a metal compound results in contamination of a robot arm, which holds and moves the semiconductor substrate, and a cassette which accommodates the semiconductor substrate during a process of transferring the semiconductor substrate to a subsequent processing step. Eventually, metal contamination spreads throughout an overall LSI fabrication process. Particularly, copper would pose an extremely serious problem during a heat treatment process because copper has a high coefficient of diffusion into a silicon oxide film, which is on the semiconductor substrate.
Heretofore, it has been customary to clean a bevel portion of a semiconductor substrate by supplying a liquid mixture of hydrofluoric acid or hydrochloric acid and hydrogen peroxide to the bevel portion from an opposite side of the semiconductor substrate, blowing a nitrogen gas to a surface of the semiconductor substrate to prevent the liquid mixture from flowing onto the surface of the semiconductor substrate, and controlling an etched depth of the bevel portion.
However, the above process is disadvantageous in that a large amount of nitrogen gas has to be supplied to prevent the liquid mixture from flowing onto the surface of the semiconductor substrate, and in that the liquid mixture needs to be supplied also in a large amount to clean the bevel portion. In presence of water and oxygen, copper instantly forms oxides. A tendency of copper to form oxides becomes more significant, particularly during a substrate drying step. Oxides of copper thus formed are mainly a mixture of cupric oxide and copper carbonate, and are likely to greatly increase a specific electric resistance of interconnections.